1. Field of the Invention
The present invention relates to a method for testing the operability of a tank shutoff valve of a fuel tank system which is controlled by valves.
2. Description of Related Art
Methods and monitoring and control systems for testing fuel tank systems are known from the related art.
Thus, for example, published German patent document DE 196 36 431 A1 discloses a method and a device for testing the operability of a tank ventilation system, in which an overpressure or partial vacuum is introduced into a tank ventilation system and the tightness of the tank ventilation system is determined from the pressure curve. The pressure curve is determined by detecting operating parameters of the pressure source upon introduction of the pressure. A method for testing the operability of a tank ventilation system of a vehicle using a tank tightness test is also disclosed in published German patent document DE 198 09 384 C2. Using a tank tightness testing device of this type, it may be reliably stated whether there is a tank leak.
More recent tank systems are equipped with an additional tank shutoff valve, which is situated between the fuel tank and an activated carbon filter, which is used for temporarily storing outgassing fuel vapors. This tank shutoff valve is normally always closed, so that significant partial vacuums or overpressures may arise in the tank system because of the leakproof tank. This valve is opened in order to regulate the pressure in the tank to a specific predefined value.
Because the tank shutoff valve represents an exhaust-relevant element, its operability must be checked.